Classless Routing Protocols are the Routing Protocols that don’t follow the Address Classes subnet masking instead favour the Variable-Length Subnet Masking (VLSM)#. All protocols will include network mask when sending the routing information to other Network Device. It is aimed to replace Classful Routing Protocols.
Examples of Classless Routing Protocols:
RIP is a #classful #Distance Vector Routing Protocol that use hop count as metric to find out the routing path. The underlying #algorithm used is the Bellman-Ford Algorithm. If the metric of route is larger than 15, RIP will count it as unreachable. Routing updates are done via broadcast IP address. It can only run on IPv4 networks, in order to run IPv6 one needs to deploy RIPng (RIP next generation) instead. There is a classless implementation of RIP: RIP version 2 (RIPv2)#.
RIPv2 is a #classless #Distance Vector Routing Protocol derived from #Routing Information Protocol (RIP) to support discontiguous network, Variable-Length Subnet Masking (VLSM)# and Classless Inter-Domain Routing (CIDR)#. It uses multicast IP addresses for routing updates as they take up less bandwidth and require less processing on other non-RIP enabled devices.
OSPF is a #Layer 3 #classless #Link-State Routing Protocol developed by Internet Engineering Task Force (IETF)# where its metric is an arbitrary value called cost (defined by RFC 2328). In Cisco, the cost calculated using bandwidth. It is secure, scalable and provides fast Convergence#. It supports both IPv4 and IPv6. The implementation of OSPF varies from vendor to vendor.
IS-IS is a #classless #Link-State Routing Protocol which has wide adoption by Internet Service Provider (ISP)#. It is a rather harden protocol to used as the attacker couldn’t break into a network routing with IS-IS using other Routing Protocol. It is available for both IPv4# and IPv6#.
By using CIDR, we could reduce the size of the Routing Table as the supernet (network that is at a higher hierarchy) is able to summarise multiple network addresses with a subnet mask that is less than the classful subnet mask. Classless Routing Protocols# will be used for routing update.
Classful Routing Protocols are the Routing Protocols# that follow the Fix-Length Subnet Masking#. However, as the networking technologies advanced, most Classful Routing Protocols are phased out in favour of Classless Routing Protocols due to the limitation of Classful Routing Protocols to travel to different Address Classes since the routing update doesn’t include the network mask.